DP_EDP_BACKLIGHT_BRIGHTNESS_MSB
if (drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
DP_EDP_BACKLIGHT_BRIGHTNESS_MSB);
if (drm_dp_dpcd_write(&intel_dp->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,